A steam turbine is a common apparatus for producing mechanical energy out of the thermal energy contained in steam. The steam is guided to the blades of the turbine and puts them in motion. For this purpose the steam can be produced for example by combustion processes. The mechanical energy can then possibly be used for propulsion or, by driving a generator, for producing electric energy.
For an optimized operation of the steam turbine, it is advantageous to balance the axial thrust of the turbine rotor. This balance can be achieved with one or several sealing bushes. Such a sealing bush has the mean diameter of the blading part, which axial thrust shall be balanced. The pressures before and after the sealing bush are the same of the corresponding blading part. The pressure before the first part is the pressure after the control stage, the pressure after the last segment of the sealing bush is the exhaust pressure.
In such a sealing bush 1, as shown in FIG. 1, steam can be extracted, as indicated by arrow 20. The sealing bush carrier 1 is installed in a steam turbine 40, its rotor-facing part 4 facing the shaft 42 of the turbine rotor 41, its housing-facing part 5 facing the turbine housing 43 respectively. The sealing bush carrier 1 comprises a hollow passage 2 which is assigned to a hollow opening 44 in the turbine housing 43. The axis 7 of the passage 2 can be thought extended in the opening 43. Therefore an extraction 20 of the steam is possible. The extracted steam can be subsequently supplied to a balancing piston (not shown). Using this piston, a balancing of the axial thrust of the turbine can be done.
However, a sealing bush according to the state of the art allows only to extract steam at one distinct pressure level along the sealing bush carrier and therefore along this part of the steam turbine. For a more effective balancing, the extraction of steam at different pressure levels can be advantageous. In particular, the balancing of the axial thrust can be done more precisely and therefore the steam turbine can be operated with higher efficiency.